(1) Field of the Invention
The present invention relates to a pipe expanding apparatus of a thin wall stainless steel pipe, which expands a pipe for forming a chevron projection portion having a chevron cross sectional shape along an outer peripheral surface of an end portion of the thin wall stainless steel pipe.
(2) Description of Related Art
With regard to a pipe expanding apparatus of a thin wall stainless steel pipe, a structure described in Japanese Examined Patent Publication No. 64-137 filed by the applicant of the subject application has been already known. As shown in FIG. 8, a pipe expanding apparatus 101 of a thin wall stainless steel pipe has a hydraulic cylinder 102, a piston rod 104 having a piston portion 103 which is slidably operated by a hydraulic pressure within the hydraulic cylinder 102, a restoring spring 105 biasing the piston rod 104 to a rear side (a right side in the drawing), a pipe expanding head 106 provided in a rear end portion of the hydraulic cylinder 102, a coupling pipe 108 coupling the piston rod 104 and a pressure application rod 107, a guide ring 110 arranged in an inner side of a fitting inner hole 109 of the pipe expanding head 106 so as to be immovable forward, a pipe expanding rubber 112 arranged between the guide ring 110 and a rubber restraining step portion 111 of the pressure application rod 107, and a female thread portion 114 engaging with a male thread portion 113 formed in an outer peripheral surface of the pipe expanding head 106, and the pipe expanding apparatus 101 is structured such as to have a ball head lock nut 117 inserting a thin wall stainless steel pipe 116 to a fitting hole 115, and is structured such that taper portions 119 and 120 are formed respectively in such a manner that a peripheral groove 118 having a chevron shaped cross section is formed in a joint portion between an inner peripheral surface of the pipe expanding head 106 and the inner peripheral surface of the ball head lock nut 117, in a state in which the pipe expanding head 106 and the ball head lock nut 117 are engaged and fixed.
The pipe expansion of the thin wall stainless steel pipe 116 by the conventional pipe expanding apparatus 101 of the thin wall stainless steel pipe as mentioned above is carried out as follows. Specifically, in a state in which a leading end portion 116a of the thin wall stainless steel pipe 116 is fitted into the fitting inner hole 109 of the pipe expanding head 106, the piston rod 104 is actuated forward, that is, to an opposite side to the thin wall stainless steel pipe 116 by a hydraulic pressure, as shown in FIG. 9. Accordingly, since the pressure application rod 107 coupled to the piston rod 104 is moved forward, the pipe expanding rubber 112 is pressed between the guide ring 110 and the step portion 111 of the pressure application rod 107, so that the pipe expanding rubber 112 is reduced in length in a back and forth direction, and swells outward in a diametrical direction. Further, since the peripheral groove 118 (refer to FIG. 8) having the chevron shaped cross section is formed in an outer periphery of the thin wall stainless steel pipe 116 extruded outward in the diametrical direction by the swelling pipe expanding rubber 112, by a taper portion 119 of the pipe expanding head 106 and a taper portion 120 of the ball head lock nut 117, the thin wall stainless steel pipe 116 swells in such a manner as to be along the peripheral groove 118 having the chevron shaped cross section, and a chevron shaped pipe expanding portion 122 is formed.
When the thin wall stainless steel pipe 116 expanded as mentioned above is connected to a joint 123, the pressure application rod 107, the pipe expanding rubber 112 and the guide ring 110 are taken out from an inner portion of the thin wall stainless steel pipe 116 after releasing the engagement between the pipe expanding head 106, and the male thread portion 113 and the female thread portion 114 of the ball head lock nut 117. Further, as shown in a right side in FIG. 10, by making the opening portion of the joint 123 be opposed to an end portion of the thin wall stainless steel pipe 116 and an opening end portion of the ball head lock nut 117 so as to engage the male thread formed in an outer periphery of the joint 123 and the female thread portion 114 of the ball head lock nut 117, as shown in a left side in FIG. 10, an inclined surface 122a of the chevron shaped pipe expanding portion 122 is pressed in a direction of the joint 123, and a gasket 121 which is previously fitted to an inner side of an opening portion of the joint 123 is crimped to another inclined surface 122b, and a disc spring 125 fitted to the outer periphery of the male thread is crimped between a projection of the joint 123 and a leading end of the ball head lock nut 117 as necessary. The disc spring 125 prevents the engagement between the joint 123 and the ball head lock nut 117 from being loosened and confirms a fastening failure by a reaction thereof. Accordingly, the thin wall stainless steel pipe 116 is securely coupled to the joint 123 without generating any fluid leakage from a connection portion to the joint 123.
In the conventional pipe expanding apparatus 101 of the thin wall stainless steel pipe as mentioned above, the pipe expanding rubber 112 swelled by the pressure application while being sandwiched between the guide ring 110 and the step portion 111 by moving forward the pressure application rod 107 in accordance with a forward movement (a left side in the drawing) of the piston rod 104 from a state in FIG. 8 to a state in FIG. 9 swells out the thin wall stainless steel pipe 116 in a chevron shape along the chevron shaped peripheral groove 118 formed by an inner peripheral surface of the pipe expanding head 106 and an inner peripheral surface of the ball head lock nut 117, whereby the pipe expanding portion 122 is formed. At this time, the pressure in an outer direction during the swelling of the pipe expanding rubber 112 also acts on the pipe expanding head 106 and the ball head lock nut 117, and a strain is generated. Due to the strain, there is such a problem that the engagement between the pipe expanding head 106, and the male thread portion 113 and the female portion 114 of the ball head lock nut 117 is hard to be disengaged, the ball head lock nut 117 opens outside so as to obstruct an engagement with the joint 123 in the later step, or the like. Further, since it is necessary to secure a necessary length for engaging and firmly attaching a male thread of the joint 123 and the female thread 114 of the ball head lock nut 117, there is such a problem that a whole of the apparatus is enlarged.
The present invention is made in view of the above problem, and provides a pipe expanding apparatus of a thin wall stainless steel pipe in which a member supporting the thin wall stainless steel pipe 116 at the time of pipe expansion of the pipe expanding head 106, the ball head lock nut 117 or the like can prevent a force from acting in an outer direction so as to prevent the strain from being generated, even when the pipe expanding rubber 112 swells. Further, the present invention provides a pipe expanding apparatus of a thin wall stainless steel pipe which can achieve a downsizing of the apparatus, and can achieve convenience for transporting in a weight saving manner.